Grain monitors for combine harvesters are known in the art. It is also known in the art to utilize a load cell as part of such a monitor wherein a Wheatstone bridge or the like is utilized to detect minute deformations of a member of the cell that occur when clean grain from an elevator of the harvester impacts or otherwise exerts a load on the member.
In installations that use load cells, the load member's own weight tends to deform the member to a slight extent, introducing errors into the output data unless the weight (tare) of the member is “zeroed out” during initial calibration of the unit. While such calibration is effective so long as the harvester remains on a level surface, problems arise when the harvest encounters up slopes or downslopes during hillside operations. Some machines have included inclinometers which detect inclination of the harvester and provide appropriate input to computers that process the information to deal with the hillside, but systems of that type can be fairly complex and costly.
The present invention provides a simple yet effective way of dealing with the hillside problem. Rather than measuring the force of the grain flow horizontally after it leaves the clean grain elevator as in some conventional systems, the present invention contemplates measuring the force vertically as it moves around the upper end of the elevator and generates a centrifugal force. The load member of the cell is arranged generally horizontally such that its weight is directly opposite to the generally vertical centrifugal force being generated by the grain flow as it changes directions from vertical to horizontal. This weight can be easily zeroed out as tare during calibration. More importantly, with this arrangement the change in tare during hillside operations is much smaller than in conventional arrangements because the change is proportional to the trigonometric cosine of the hillside angle rather than the sine. Prior art devices which essentially measure the flow force horizontally introduce an error that is proportional to the change of the sine of the hillside angle.